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3 | <HEAD> | |
4 | <TITLE>Stream Offsets</TITLE> | |
5 | <LINK REL="stylesheet" HREF="../../../../boost.css"> | |
6 | <LINK REL="stylesheet" HREF="../theme/iostreams.css"> | |
7 | </HEAD> | |
8 | <BODY> | |
9 | ||
10 | <!-- Begin Banner --> | |
11 | ||
12 | <H1 CLASS="title">Stream Offsets</H1> | |
13 | <HR CLASS="banner"> | |
14 | ||
15 | <!-- End Banner --> | |
16 | ||
17 | <DL class="page-index"> | |
18 | <DT><A href="#overview">Overview</A></DT> | |
19 | <DT><A href="#acknowledgments">Acknowledgments</A> | |
20 | <DT><A href="#headers">Headers</A></DT> | |
21 | <DT><A href="#reference">Reference</A></DT> | |
22 | </DL> | |
23 | ||
24 | <HR> | |
25 | ||
26 | <A NAME="overview"></A> | |
27 | <H2>Overview</H2> | |
28 | ||
29 | <P> | |
30 | The header <A CLASS="header" HREF="../../../../boost/iostreams/positioning.hpp"><CODE><boost/iostreams/positioning.hpp></CODE></A> provides the definition of the integral type <CODE>boost::iostreams::stream_offset</CODE>, capable of holding arbitrary stream offsets on most platforms, together with the definition of two functions, <CODE>offset_to_position</CODE> and <CODE>position_to_offset</CODE>, for converting between <CODE>stream_offset</CODE> and <CODE>std::streampos</CODE>. | |
31 | </P> | |
32 | ||
33 | <P> | |
34 | The type <CODE>std::streampos</CODE> is required to be able to hold an arbitrary stream position, but it is not an intergral type. Although <CODE>std::streampos</CODE> is interconvertible with the integral type <CODE>std::streamoff</CODE>, the conversion from <CODE>std::streampos</CODE> to <CODE>std::streamoff</CODE> may not be faithful for large (64-bit) values. The integral type <CODE>boost::iostreams::stream_offset</CODE> is intended as a replacement for <CODE>std::streamoff</CODE>, with the implicit conversions to and from <CODE>std::streampos</CODE> being replaced by explicit conversion functions. | |
35 | </P> | |
36 | ||
37 | <P> | |
38 | The implementation of <CODE>offset_to_position</CODE> and <CODE>position_to_offset</CODE> relies on implementation defined behavior, and is guaranteed to work correctly for large values only for standard libraries which define <CODE>std::streamoff</CODE> to be 64-bit type or for which the Boost Iostreams library has been explicitly configured. | |
39 | </P> | |
40 | ||
41 | <A NAME="acknowledgments"></A> | |
42 | <H2>Acknowledgments</H2> | |
43 | ||
44 | <P>Gareth Sylvester-Bradley suggested the treatment of large stream offsets used by the Boost Iostreams library and supplied the implementation of <CODE>offset_to_position</CODE> and <CODE>position_to_offset</CODE> used with the Dinkumware standard library.</P> | |
45 | ||
46 | <A NAME="headers"></A> | |
47 | <H2>Headers</H2> | |
48 | ||
49 | <DL class="page-index"> | |
50 | <DT><A CLASS="header" HREF="../../../../boost/iostreams/positioning.hpp"><CODE><boost/iostreams/positioning.hpp></CODE></A></DT> | |
51 | </DL> | |
52 | ||
53 | <A NAME="reference"></A> | |
54 | <H2>Reference</H2> | |
55 | ||
56 | <A NAME="synopsis"></A> | |
57 | <H4>Synopsis</H4> | |
58 | ||
59 | <PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams { | |
60 | ||
61 | <SPAN CLASS='keyword'>typedef</SPAN> <A CLASS='documented' HREF='../../../integer/doc/html/boost_integer/cstdint.html' TARGET='_top'>boost::intmax_t</A> stream_offset; | |
62 | std::streampos <A CLASS='documented' HREF='#offset_to_position'>offset_to_position</A>(stream_offset n); | |
63 | stream_offset <A CLASS='documented' HREF='#position_to_offset'>position_to_offset</A>(std::streampos pos); | |
64 | ||
65 | } } <SPAN CLASS='comment'>// End namespace boost::io</SPAN></PRE> | |
66 | ||
67 | <A NAME="offset_to_position"></A> | |
68 | <H4>Function template <CODE>offset_to_position</CODE></H4> | |
69 | ||
70 | <PRE CLASS="broken_ie">std::streampos offset_to_position(stream_offset n);</PRE> | |
71 | ||
72 | <P>Returns a <CODE>std::streampos</CODE> representing the <CODE>n</CODE><I>th</I> position in a stream.</P> | |
73 | ||
74 | <A NAME="position_to_offset"></A> | |
75 | <H4>Function template <CODE>position_to_offset</CODE></H4> | |
76 | ||
77 | <PRE CLASS="broken_ie">stream_offset position_to_offset(std::streampos pos);</PRE> | |
78 | ||
79 | <P>Returns a <CODE>stream_offset</CODE> representing the same character position as <CODE>pos</CODE>, disregarding any code-conversion state.</P> | |
80 | ||
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85 | <P CLASS="copyright">© Copyright 2008 <a href="http://www.coderage.com/" target="_top">CodeRage, LLC</a><br/>© Copyright 2004-2007 <a href="http://www.coderage.com/turkanis/" target="_top">Jonathan Turkanis</a></P> | |
86 | <P CLASS="copyright"> | |
87 | Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at <A HREF="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</A>) | |
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